Many organisations now require that CCTV video images are recorded and archived continuously from all cameras for 90 days or more.
In large systems this can create a significant storage requirement. This is compounded by users wanting to store video at the highest quality and maximum frame rate, particularly where CCTV footage is required for evidential purposes.
The storage element of a large IP-CCTV system can therefore dominate the overall cost of the system, both up-front costs and lifecycle costs as hard drives will often need to be replaced over the life of the project. With potentially large amounts of data being stored, the technology behind the compression employed and the architecture of the storage solution are critical to ensure these extended recording times can be accommodated. Similarly, the security of the stored data is important so that individual disk and equipment failures do not result in data loss.
The Scale of the Problem
The factors that affect how much disc storage is required are video resolution, frame-rate, number of cameras and the quality of the compression technology deployed. So when comparing systems the main variable is the compression technology, as all other factors are constant.
The way in which video is compressed can make a significant difference to the storage requirements. The following worked example demonstrates the storage requirements for a typical system, comparing equipment that has an average compression with the very best that is available.
The amount of digital data generated by a single camera:
Best compression: 20 gigabytes/day
Average compression: 40 gigabytes/day
This doesn’t at first seem unmanageable since hard disk storage is inexpensive and 750 Gigabyte disks are readily available. However, assume a system with 100 cameras and the storage becomes:
Best compression: 2 terabytes/day
Average compression: 4 terabytes/day
Archiving recordings for 90 days gives:
Best compression: 180 terabytes
Average compression: 360 terabytes
The difference between an average compression and the best is 180 Terabytes of extra storage and that’s just for a relatively small system of 100 cameras.
NVR Performance
When it comes to storage, CCTV systems are very different to IT systems. The amount of data coming from the cameras to the NVRs is huge and continuous. The amount of data coming from the NVR to the users is very low and periodic. The workload is constant, i.e. the rate of writing data to the disk is constantly high, not in bursts as with typical IT applications.
The processing overhead for writing and reading the video streams to disk is therefore an important factor in the overall performance of the NVR. There can be a considerable difference in this overhead between different vendors of NVR software. Software which can minimise this processing will be able to handle many more camera streams per NVR. The best NVR server software on the market has such a low CPU loading that 200 camera streams can be recorded on the lowest specification server PC. Therefore, in a large system with a 90 day recording requirement, the limitation on the server is its storage, not its processing power.
The storage architecture for CCTV systems can be categorised as either centralised or distributed.
Centralised Storage Architectures
A typical example of such as system would be a Casino, where a high density of cameras are located in one building. The NVRs would be located in one central IT facility, with a central network switch. In this situation all of the video could be recorded on one server, however, this would almost certainly be storage limited, not CPU limited.
Using the worked example above with a 100 camera system, one option would be to use ten NVR servers each fitted with an 18 Terabyte disk array, assuming the system has the best compression technology available. This is still a lot of hardware, but because the CPU utilisation is low, virtual servers can be deployed. Leading NVR vendors can run their software under applications such as VMware (see panel ‘Virtual servers’) allowing ten virtual servers to be configured on one physical server, considerably reducing equipment costs. In reality the typical casino uses between 500 and 1000 cameras, so this approach is an important factor in keeping down costs.
Distributed Storage Architectures
A typical example of such a system would be a rail network that could have 200 cameras located across 25 stations with on average eight cameras per station, with some stations only having four cameras. In this situation what is needed is a small, flexible storage which can use the right amount of storage for the right amount of cameras.
For this example, assume a 500 gigabytes/camera is required for 90 day recording. An NVR with two terabytes could be deployed at each station, one NVR per four cameras. The smaller stations would have one NVR with the larger ones having five, a total of 50 NVRs for all 200 cameras. This would significantly reduce the bandwidth required from the network. The flexibility of the virtual matrix created by the IP Video system means any user with the right permissions could view and analyse recorded video from any NVR, no matter where on the network they are located.
If PC based servers were used in the example above, then 50 separate servers would be required each with their own local attached storage, which comes at a significant cost. An alternative would be to use dedicated, standalone NVR units which have the processing hardware and storage in a single compact unit. These are considerably less expensive than a PC server and equivalent storage.
In order to satisfy different types of applications a vendor needs to be able to provide a flexible and scalable recording solution that can use both PC server configurations and dedicated NVR units as appropriate.
Data Security
With so much valuable data being recorded, it’s important to consider NVR security and reliability. Most PC based NVR servers will deploy RAID disk arrays. A Redundant Array of Independent Drives (RAID) is an umbrella term for computer data storage schemes that divide and/or replicate data among multiple hard drives. There are different RAID levels, giving different levels of protection. In a RAID 5 configuration, for example, the data is striped across three separate disks. If any disk fails no data is lost and the computer can continue without interruption.
To take NVR security a level further, dedicated NVR hardware can be deployed. These standalone robust hardware units can have redundant power supplies and network connections, RAID configurations and hot-swappable drives. An IP Video system that deploys standalone NVR units should also have a flexible NVR backup strategy. For example if an NVR failure is detected by the system software then recordings can be automatically switched to a backup NVR or distributed amongst other NVRs in the system. Like RAID configurations in PCs, NVRs can be mirrored, with the same video being recorded on two NVRs simultaneously, providing the highest level of security.
DVR vs NVR
What about traditional analogue CCTV systems that use DVRs? Firstly, it is important to differentiate between DVRs and NVRs, as both are often termed ‘digital’. A DVR digitally compresses analogue video feeds and stores them on a hard-drive, the term ‘digital’ referring to the compression and storage technology, not the transmitted video images. The DVR therefore has to be located near the analogue feeds and is only really used in centralised architectures. In contrast, an NVR stores digital images directly from the IP-network and can be located anywhere on the network. It is therefore typical for a DVR to be located centrally, close to the analogue matrix and control room equipment. As the size of the system increases and the number of recording days increases there is no other option but to keep adding additional DVRs. This in itself is not a problem other than the cost overhead associated with the DVR. A high-end DVR would typically be able to record 16 cameras on to a 2-terabyte disk. Using our worked example for a casino and assuming the very best compression available this would give just over 6 days of recording for all 16 cameras or 90 days for just one camera. Clearly DVR technology is simply too expensive for large scale digital recording applications.
Reducing the Amount of Video
There are a number of compression standards currently employed in IP Video systems. H.264 is the latest official video compression standard, which follows on from the highly successful MPEG-2 and MPEG-4 video standards and offers improvements in both video quality and compression. The most significant benefit for IP Video systems is the ability to deliver the same high-quality, low latency, digital video with savings of between 25 and 50 per cent on bandwidth and therefore on the storage requirements. By selecting a system based on H.264 further savings on storage can be achieved. Even though H.264 is more efficient than MPEG-4, there are still differences between vendors’ implementation of the standard and hence the amount of storage required.
There is no point in recording video from a camera at full frame rate if there is nothing in the scene to record. By using applications such as IndigoVision’s unique Actively Controlled Framerate (ACF), the amount of video and hence storage can be significantly reduced. When a scene is inactive the video can be streamed at a much lower frame rate. As soon as the motion analysis software detects movement the video is streamed at full frame rate.
The requirement to record CCTV images for 90+ days will have a large impact on the storage requirement of the project and hence the cost. With larger systems the inflexibility and costs involved with an analogue/DVR solution means IP video is the only way forward.
Running a self storage facility, I can tell you that I can relate all too well to this article! Making sure that my clients’ items are safe in their self storage units is no joke and keeping the CCTV footage isn’t either. I’m happy to read that there are so many areas that we can look at like the video quality and frames per second that we can work on to make it a tad more cost effective for storage!
http://supercheapselfstorage.com.au/facilities/gold-coast/self-storage/michael-maloney/
michaelmaloney1
Hi we have 900 IP cameras & 325 NVRs at different location in India. Now Customer wants to Auto Archive of recorded in each location to Central site in low resolution.
Can u pls give us a solution.
Google
Usually posts some extremely intriguing stuff like this. If youre new to this site.
35 CAMMERA CCTV SYSTEM. TO STORE DATA FPR AT LEAST90DAYS
what is the price?
how is keep the backup system 180days use 32ch &16 dvr totaly camera 50.
what is Nas system.
my camera is only recording at just 10 days
how i achive it to 90+ days